| Langensee | |
| Location: | Schleswig-Holstein, Germany |
| Coords: | 54.1628°N 10.4839°W |
| Inflow: | Schwentine from the Dieksee |
| Outflow: | Schwentine to the Behler See |
| Cities: | Plön |
| Elevation: | 22m (72feet) |
| Area: | 33ha |
| Pushpin Map: | Germany Schleswig-Holstein |
| Max-Depth: | 8m (26feet) |
The Langensee is a lake in the North German lakeland region of Holstein Switzerland.It lies on the River Schwentine between the lakes of Dieksee (upstream) and Behler See (downstream). It covers an area of 33ha, is up to 8 metres deep and lies at a height of .